Zuo Guoping, Wang Hongping, Lan Lei, Zhang Yonggang, Zuo Yinhui, Yang Liu, Wang Chaofeng, Pang Xu, Song Xu, Yang Meihua
PetroChina Hangzhou Research Institute of Geology, Hangzhou, 310023, China.
State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Chengdu University of Technology, Chengdu, 610059, China.
Sci Rep. 2023 Jul 31;13(1):12369. doi: 10.1038/s41598-023-39702-5.
The Santos Basin, located in the southeastern waters of Brazil, is a passive continental margin basin with the most abundant deepwater petroleum resources in the world discovered to date. However, few studies have been conducted on the present geothermal fields of the Santos Basin, which severely restricts the oil and gas resource evaluation of the basin. This study first utilizes 35 temperature data from 16 post-salt drilling wells and 370 temperature data from 31 pre-salt drilling wells to calculate the post-salt and pre-salt geothermal gradients and terrestrial heat flows in the Santos Basin. Then, the basin simulation software BasinMod 1D is used to quantitatively evaluate the impacts of salt rock sedimentation on the present geothermal fields and the maturity of pre-salt hydrocarbon source rocks. The results demonstrate that the present post-salt geothermal gradient in the Santos Basin is 2.20-3.97 °C/100 m, with an average value of 2.99 °C /100 m, and the post-salt terrestrial heat flow is 54.00-97.32 mW/m, with an average value of 73.36 mW/m, while the present pre-salt geothermal gradient is 2.21-2.95 °C/100 m, with an average value of 2.53 °C/100 m, and the pre-salt terrestrial heat flow is 61.85-82.59 mW/m, with an average value of 70.69 mW/m. These values are characteristic of a low-temperature geothermal field in a zone with a stable structure. The sedimentation of the salt rock causes a decrease in the temperature of the pre-salt strata, which inhibits pre-salt hydrocarbon source rock maturity, with an inhibition rate of up to 1.32%. The inhibition degree decreases with increasing salt rock thickness. At the same time, the salt rock thickness is positively correlated with the present surface heat flow. The unique distribution of the salt rock and related salt structures lead to present terrestrial heat flow differences among different structural units in the basin. This study is of great significance for evaluating and exploring the pre-salt oil and gas resources in the Santos Basin.
桑托斯盆地位于巴西东南部海域，是一个被动大陆边缘盆地，是迄今为止世界上发现的深水石油资源最为丰富的盆地。然而，针对桑托斯盆地现今地温场开展的研究较少，这严重制约了该盆地的油气资源评价。本研究首先利用16口盐下钻井的35个温度数据以及31口盐上钻井的370个温度数据，计算桑托斯盆地盐下和盐上的地温梯度以及大地热流。然后，运用盆地模拟软件BasinMod 1D定量评估盐岩沉积对现今地温场以及盐下烃源岩成熟度的影响。结果表明，桑托斯盆地现今盐下地温梯度为2.20～3.97℃/100m，平均值为2.99℃/100m，盐下大地热流为54.00～97.32mW/m，平均值为73.36mW/m；而现今盐上地温梯度为2.21～2.95℃/100m，平均值为2.53℃/100m，盐上大地热流为61.85～82.59mW/m，平均值为70.69mW/m。这些数值具有稳定构造区低温地温场的特征。盐岩沉积导致盐下地层温度降低，抑制了盐下烃源岩成熟，抑制率高达1.32%。抑制程度随盐岩厚度增加而减小。同时，盐岩厚度与现今地表热流呈正相关。盐岩及相关盐构造的独特分布导致盆地内不同构造单元现今大地热流存在差异。本研究对于评价和勘探桑托斯盆地盐下油气资源具有重要意义。
